According to a conventional tire mounter for mounting a tire on a wheel, a tire bead press roller to be pressed against an upper bead part side of the tire and a tire presser to be pressed against the upper bead part side of the tire are used. The tire bead press roller is turned from a state where the tire is normally temporarily fitted on the wheel aslant, while the upper and the lower bead parts of the tire are compelled to contact the outer periphery (edge part) of the wheel to be slid by two motions (two times mounting operation) or one motion (one time mounting operation), thereby mounting the tire on a predetermined position of the wheel. Such a conventional mounter is disclosed, for example, in JP 11-192823 A.
Meanwhile, in the foregoing conventional case where the bead parts of the tire to be mounted are forcibly slid on the periphery (edge part) of the wheel while being compelled to contact the same, a friction force of the tire when contacting the wheel becomes considerably large and brings about a concern that the bead parts are prone to be damaged.
For example, in the case of a small-sized and thin tire, even if the bead parts of the tire are forcibly slid, they are not much damaged, while in the case of a large-sized and thick tire (radial tire, low-profile tire, and so forth), the bead parts are hard and have a considerable rigidity and a large load (friction force) is generated when the bead parts contact the wheel. Particularly, since many core members such as steel wires are normally embedded in the tire, particularly in the case of a rubber tire, if the tire is forcibly compelled to contact the wheel, it was found from the experiment made by the present inventor that a load applied to the tire when the tire contacts the wheel in the case of mounting the tire T on the wheel H (hereinafter referred to as contact load) reaches about 100 Kg to the maximum of about 340 Kg (the maximum value in a specific direction of three dimensional directions of x, y and z when the contact load is divided into three dimensional directions).
The inventor of this application studied this point more in detail and it was found that if the contact load is large, especially the upper bead part of the tire is prone to be damaged with ease. The outer side of the bead part has sufficient strength since it is exposed to the outside, while the inner side of the bead part does not have sufficient strength such as the strength of the outer side of the bead part, because it is positioned inside the wheel when the tire is mounted on the wheel.
Accordingly, in the case of the tire which was temporarily fixed on the wheel aslant, when the lower bead part of the tire is mounted on the wheel, a strong outer side of the lower bead part is compelled to contact the outer periphery of the wheel, so that the tire is not damaged significantly. However, when the upper bead part of the tire is mounted on the wheel, an inner side of the upper bead part (part which is weak in strength) is compelled to contact the outer periphery of the wheel, the level of damage of the tire is prone to be large. It is more troublesome that once the tire is mounted on the wheel, the level of the damage (generation of cracks and so forth) at the inner side of the bead part of the tire cannot be seen from the outside so that such damage is hardly found out and forms hidden defects. The cracks of the tire grow with time, and it is found when abnormality occurs to the tire during the traveling of the tire.
Accordingly, it is conceived that the interval (gap) between the wheel and the tire bead press roller is made large in order to reduce the contact load of the tire. If this interval is made large, the biting of the tire relative to the wheel becomes inferior and causes a new problem that an excellent mounting of the tire is not guaranteed.
To that end, it is adjusted in the conventional mounter that the speed of the tire bead press roller to approach the wheel is compelled to slow down in order to optimize the interval between the wheel side and the tire bead press roller, thereby minimizing the contact load of the tire. On the contrary, when the wheel side, namely, the lift table side, approaches the tire bead press roller, the approaching speed is compelled to slow down in front of the tire bead press roller. Alternatively, both the approaching speed of the tire bead press roller and that of the lift table side are controlled, or dimensions of wheels (because in the case of the wheels manufactured mainly by moulding, dimensions are varied widely) are measured beforehand. The information of the measurement is used for controlling both of the approaching speeds. In this case, additional steps are increased, inevitably lowering the efficiency caused by slowing down the speed when mounting the tire on the wheel.
Accordingly, the inventor of this application provides a bead guide plate which serves as a guide pallet for reducing friction and which is turned while being positioned on the upper surface side of the wheel in order to reduce the contact load of the bead part of the tire temporarily fixed on the wheel aslant at the non-mounting side of the tire when mounting the tire on the wheel. The bead guide plate is, therefore, inserted into a bead part of the tire which is positioned at the inner side of the outer peripheral surface of the wheel at the non-mounting side, thereby causing the bead guide plate to turn ahead of the bead part of the tire at the non-mounting side of the tire. As a result, when the bead part of the tire at the non-mounting side is pressed by the tire bead press roller, it is guided to be slid from the surface side of the bead guide plate which is positioned in the manner of overlapping the upper surface side of the wheel, so that the tire can be mounted smoothly on the wheel with minimum contacts to the wheel side. Further, it was found that the contact load was significantly reduced (the maximum value of the contact value in a specific direction of three dimensional directions of x, y and z is reduced to about 20 Kg, and will be described in detail later).